15.10.Qd Quantum dots

Dephasing-assisted transport in linear triple quantum dots

Date: 
2016-06-03
Author(s): 

L.D. Contreras-Pulido, M. Bruderer, S.F. Huelga and M.B. Plenio

Reference: 

New J. Phys. 16 113061

Environmental noise usually hinders the efficiency of charge transport through coherent quantum systems; an exception is dephasing-assisted transport (DAT). We show that linear triple quantum dots in a transport configuration and subjected to pure dephasing exhibit DAT if the coupling to the drain reservoir exceeds a threshold. DAT occurs for arbitrarily weak dephasing and the enhancement can be directly controlled by the coupling to the drain. Moreover, for specific settings, the enhanced current is accompanied by a reduction of the relative shot noise.

Efficient controlled-phase gate for single-spin qubits in quantum dots

Date: 
2011-03-10
Author(s): 

T. Meunier, V.E. Calado, L.M.K. Vandersypen

Reference: 

Physical Review B 83, 121403

Two-qubit interactions are at the heart of quantum information processing. For single-spin qubits in semiconductor quantum dots, the exchange gate has always been considered the natural two-qubit gate. The recent integration of a magnetic field or g-factor gradients in coupled quantum dot systems allows for a one-step, robust realization of the controlled-phase (C-phase) gate instead.

Quantum-Dot-Spin Single-Photon Interface

Date: 
2010-07-15
Author(s): 

S. T. Yılmaz, P. Fallahi, and A. Imamoğlu

Reference: 

Phys. Rev. Lett. 105, 033601 (2010)

Using background-free detection of spin-state-dependent resonance fluorescence from a single-electron charged quantum dot with an efficiency of 0.1%, we realize a classical single spin-photon interface where the detection of a scattered photon with 300 ps time resolution projects the quantum dot spin to a definite spin eigenstate with fidelity exceeding 99%. The bunching of resonantly scattered photons reveals information about electron spin dynamics.

Crystal Phase Quantum Dots

Date: 
2010-03-05
Author(s): 

N. Akopian, G. Patriarche, L. Liu, J.-C. Harmand and V. Zwiller

Reference: 

Nano Lett., 2010, 10 (4), pp 1198–1201

In semiconducting nanowires, both zinc blende and wurtzite crystal structures can coexist. The band structure difference between the two structures can lead to charge confinement. Here we fabricate and study single quantum dot devices defined solely by crystal phase in a chemically homogeneous nanowire and observe single photon generation.

Giant Stark effect in the emission of single semiconductor quantum dots

Date: 
2010-07-19
Author(s): 

Anthony J. Bennett, Raj B. Patel, Joanna Skiba-Szymanska, Christine A. Nicoll, Ian Farrer, David A. Ritchie, and Andrew J. Shields

Reference: 

Appl. Phys. Lett. 97, 031104 (2010)

We study the quantum-confined Stark effect in single InAs/GaAs quantum dots embedded within a AlGaAs/GaAs/AlGaAs quantum well. By significantly increasing the barrier height we can observe emission from a dot at electric fields of 500 kV cm−1, leading to Stark shifts of up to 25 meV. Our results suggest this technique may enable future applications that require self-assembled dots with transitions at the same energy.

 

Nonequilibrium transport theory of the singlet-triplet transition: Perturbative approach

Date: 
2010-10-28
Author(s): 

B. Horváth, B. Lazarovits, G. Zaránd

Reference: 

Phys. Rev. B 82, 165129 (2010)

We use a simple iterative perturbation theory to study the singlet-triplet (ST) transition in lateral and vertical quantum dots, modeled by the nonequilibrium two-level Anderson model. To a great surprise, the region of stable perturbation theory extends to relatively strong interactions, and this simple approach is able to reproduce all experimentally observed features of the ST transition, including the formation of a dip in the differential conductance of a lateral dot indicative of the two-stage Kondo effect, or the maximum in the linear conductance around the transition point.

Spin-Dependent Transport through Quantum-Dot Aharonov-Bohm Interferometers

Date: 
2010-10-29
Author(s): 

B. Hiltscher, M. Governale, and J. König

Reference: 

Phys. Rev. B 82, 165452 (2010)

We study the influence of spin polarization on the degree of coherence of electron transport through interacting quantum dots. To this end, we identify transport regimes in which the degree of coherence can be related to the visibility of the Aharonov-Bohm oscillations in the current through a quantum-dot Aharonov-Bohm interferometer with one normal and one ferromagnetic lead. For these regimes, we calculate the visibility and, thus, the degree of coherence, as a function of the degree of spin polarization of the ferromagnetic lead.

Charge and spin dynamics in interacting quantum dots

Date: 
2010-04-28
Author(s): 

J. Splettstoesser, M. Governale, J. König, and M. Büttiker

Reference: 

Phys. Rev. B 81, 165318 (2010)

The transient response of a quantum dot with strong Coulomb interaction to a fast change in the gate potential, as well as the stationary ac response to a slow harmonic variation in the gate potential are computed by means of a real-time diagrammatic expansion in the tunnel-coupling strength. We find that after a fast switching, the exponential relaxation behavior of charge and spin are governed by a single time constant each, which differ from each other due to Coulomb repulsion. We compare the response to a step potential with the RC time extracted from the ac response.

Interference and Interaction Effects in Adiabatic Pumping through Quantum Dots

Date: 
2010-02-01
Author(s): 

B. Hiltscher, M. Governale, and J. König

Reference: 

Phys. Rev. B 81, 085302 (2010)

In order to investigate the effects of interference and interaction in adiabatic pumping, we consider an Aharonov-Bohm (AB) interferometer with a quantum dot embedded either in one or in both arms. We employ a real-time formalism and we perform an expansion both in the tunnel-coupling strengths between dot and leads and in the pumping frequency, taking into account the Coulomb interaction nonperturbatively. We find that pumping in a single-dot AB interferometer has a peristaltic but phase-coherent character.

Prediction of resonant all-electric spin pumping with spin-orbit coupling

Date: 
2010-07-28
Author(s): 

V. Brosco, M. Jerger, P. San Jose, G. Zarand, A. Shnirman, and G. Schön

Reference: 

Phys. Rev. B 82, 041309(R) (2010)

All-electric devices for the generation and filtering of spin currents are of crucial importance for spintronics experiments and applications. Here we consider a quantum dot with spin-orbit interaction coupled to two metallic leads. After analyzing, the conditions for having nonvanishing spin currents in an adiabatically driven two-terminal device, we focus on a dot with two resonant orbitals and we show by specific examples that both spin filtering and pure spin current generation can be achieved. Finally, we discuss the effect of the Coulomb interaction.

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